This invention relates to an electronic drive unit assembly for a heavy-duty vehicle and more particularly to a drive unit assembly that incorporates an electric motor into each wheel spindle to drive a deep ratio reduction gear assembly at each driven wheel end on a heavy-duty vehicle.
Gear reduction assemblies are used in many different types of vehicles to provide a desired drive torque and speed output at a vehicle wheel. Heavy-duty off-road vehicles such as lift trucks, container handlers, rough terrain cranes, front end loaders, mining trucks, log haulers, etc., often require significant reductions in order to achieve high output torque at the wheel to operate on adverse ground conditions. Traditionally, these vehicles are driven by planetary axles that include planetary gear reduction assemblies.
Planetary axles include a center axle housing with wheel ends mounted at each end of the housing. A center carrier is enclosed within the axle housing and is coupled to an input from a vehicle engine and transmission. The carrier drives a pair of axle shafts that extend to each wheel end. Each wheel end includes a planetary gear reduction assembly that is driven by one of the axle shafts.
A typical planetary gear reduction assembly includes an internally toothed ring gear, a sun gear that is centrally positioned within the ring gear, and a plurality of planet gears in meshing engagement with both the sun and ring gears. The sun gear is driven by an axle shaft and the reaction between the sun, planet, and ring gears results in rotation of the wheel at a desired speed and torque.
One disadvantage with this traditional planetary gear configuration is that deep gear reductions, such as 200:1, are not available at the wheel end due to packaging constraints. Also, planetary axles for heavy duty vehicles are heavy and require powerful engines that generate pollutants, which are undesirable. As the industry moves toward lower emission requirements, alternative ways to power heavy-duty off-road vehicles are being explored.
Accordingly, it is desirable to provide a drive unit assembly that reduces emissions, reduces weight, and which provides a wider range of deep gear reductions, as well as overcoming the other deficiencies in the art outlined above.
An electronic drive unit assembly independently drives each driven wheel on a heavy-duty vehicle. Each electronic drive unit assembly includes an electric motor mounted within a spindle that is mounted to a vehicle structure such as the frame or suspension. The motor is mounted within a chamber formed inside the spindle and is protected from external contaminants. A wheel hub is mounted for rotation relative to the spindle and is driven by the motor. The motor has an output shaft that is concentric with the wheel. The output shaft is coupled to a reduction gear assembly that produces a desired output torque at the wheel, and which is operatively coupled to drive the wheel hub.
In the preferred embodiment, the reduction gear assembly is a deep ratio gear reduction assembly that is compatible with a high-speed electric motor to produce a desired wheel output torque and speed. The gear reduction assembly includes an inner ring gear that is mounted to the spindle and an outer ring gear that is mounted to or formed within the wheel hub. The reduction gear assembly further includes a plurality of inner planet gears that are in meshing engagement with the inner ring gear and a plurality of outer planet gears that are in meshing engagement with the outer ring gear. A planetary spider assembly interconnects the inner and outer planet gears such that each one of the inner planet gears is paired with one of the outer planet gears. The inner and outer planet gears in each pair are rigidly mounted on a common pinion shaft fixed to a spider body such that the inner and outer planet gears turn with the spider at the same speed about an axis of rotation. The inner planet gears have a first predetermined number of teeth and the outer planet gears have a second predetermined number of teeth that is different than the first predetermined number of teeth to achieve the desired gear reduction ratio.
In one embodiment, the motor indirectly drives the planetary spider assembly via a sun gear configuration. A sun gear is operatively coupled to the motor output shaft and is in meshing engagement with the inner planet gears, which are in meshing engagement with the inner ring gear. The sun gear drives the inner planet gears, which drive the planetary spider, resulting in the outer planet gears driving the outer ring gear.
In another embodiment, the motor directly drives the planetary spider assembly. The planetary spider includes a spider body with a central bore and a plurality of radial bores for mounting the pinion shafts. The output shaft is in driving engagement with the spider body via the central bore. As the spider body rotates, the inner planet gears react against the inner ring gear and the outer planet gears react against the outer ring gear to rotate the wheel hub.
The subject invention provides a drive unit assembly that reduces emissions by providing electric drive at each driven wheel, reduces weight by eliminating the need for a planetary axle assembly, and which provides a wider range of deep gear reductions. These and other features of the present invention can be best understood from the following specifications and drawings, the following of which is a brief description.